Since I'm on an animal kick here, I thought I'd just throw out there that I made a pretty interesting discovery with cats. If you want to do something that will get your cat to play-even an older cat-buy a bag of soft peppermint. Not the sticks, or the hard discs, but the kind of barrel shaped pieces that are soft, and come individually wrapped. I don't know whether its the scent or the red-and-white striped colors, but my cat goes wild over them. I tend to think its mostly the scent, because after she tears the paper open she seems more attracted to the empty wrapper than she does the loose peppermint candy. I have to take it away from here as I'm afraid she'll swallow it. She's play with the loose candy, but not as much, because she doesn't like to pick it up in her mouth due to the strong and to her doubtless overpowering taste.
But, for what its worth, it works as good or better than catnip or anything else I've ever found.